I. Field of the Invention
The present invention relates to a lighting control system for controlling the intensity of artificial illumination in order to automatically supplement natural illumination present in an area of concern. The total level of illumination is generally maintained constant, and the level of this constant illumination may be adjusted.
II. Description of the Prior Art
Fluorescent lighting fixtures and incandescent lighting fixtures are generally used for providing artificial illumination within modern office buildings. Architectural and economic limitations on the construction of new commercial buildings generally dictate that the office space include a suspended ceiling or false ceiling which includes suspended lighting fixtures, generally of the fluorescent type. The space between the suspended ceiling and the actual ceiling is generally reserved for ducting for air-conditioning and heating as well as electrical service for the lighting fixtures. The lighting fixtures are generally arranged in modular forms, with each of the illumination modules being independently controlled by a power switch. These power switches generally are of the on-off variety which merely remove power from the lights when the illuminated area is no longer in use by the occupants thereof. Continuously variable lighting controls are not frequently utilized by architects and building designers since they are aware that the occupants of the building will infrequently adjust the level of illumination, such as only once or twice per day in response to the sun being obscured by continuous layers of clouds, smog, fog, etc. The occupants of the office area generally will not devote the time and effort to continuously adjust the level of artificial illumination responsive to the sun being infrequently obscured for short periods of time by clouds, etc.
Most modern office buildings have modular lighting systems in which one switch controls from between 1,000 to 1,600 watts of artificial illumination coupled to a 110 volt or 277 volt 60-cycle source of electrical power. Careful design and layout of the office area can define these illumination modules into areas which generally receive similar amounts of natural sunlight, such as through windows, skylights, etc. If areas receiving similar amounts of natural illumination are defined, then it may be possible to sense the level of natural illumination and use the artificial illumination only to supplement the natural illumination in order to maintain a relatively constant illumination over the area at all times. In this manner areas relatively close to outward facing windows may require little additional illumination, while areas substantially separated from outwardly facing windows may require nearly continuous illumination. Office areas having no exposure to natural illumination would of course not benefit from the presence of an automatic control circuit, since the control circuit would maintain a constant level of illumination.
The present invention will be discussed assuming that modern lighting system techniques are utilized in the design of the typical office area. One example of these modern techniques are discussed in U.S. Pat. No. 4,001,571, issued to Martin. However, various other circuit branches or modular design techniques may be utilized without departing from the spirit and scope of the present system.
Denger, in U.S. Pat. No. 3,458,770, discloses an automatic lighting control system for use with controlling the exposure of photosensitive paper. The system includes a bridge circuit having a photocell therein, with the output of the photocell being adjustable so as to interrupt the flow of electrical energy to an artificial source of illumination. The power is applied to the artificial source of illumination when the level of illumination falls below a single desired point, while power is interrupted when the level of illumination exceeds the predetermined level. An integrating circuit is utilized to equalize variations in illumination produced by the artificial source over an extended period of time.
Dubot, in U.S. Pat. No. 3,961,183, discloses a photosensitive detector which is utilized in a simple voltage divider for sensing the relative level of illumination incident upon an area of interest. The non-bridged output of the photo-detector is coupled to the input of an analog circuit which in turn controls the supply of electrical energy to a single direction electrical motor. The motor sequentially closes switch contacts for coupling electrical energy to artificial illuminators. This system does not provide a tolerance interval over which the level of artificial illumination is acceptable, and apparently the motor can be driven only in a single direction.
Fisher, in U.S. Pat. No. 2,920,247, discloses a circuit utilizing a tube-type multivibrator which is driven into oscillation by the incidence of light upon a photosensitive detector coupled to the grids thereof. As the multivibrator begins to oscillate, the output power from the multivibrator is utilized to control the passage of electrical energy through a control relay, such as the type which may be utilized to supply electrical energy to the headlights of an automobile.
Long, in U.S. Pat. No. 2,078,677, discloses an artificial lighting display apparatus which is actuated when the level of natural light falls below a predetermined limit. As the device is actuated, the light sensor gradually illuminates and then gradually reduces the illumination from an artificial source of light of one color, and then periodically provides electrical energy to other colored sources of artificial illumination so as to artificially illuminate a subject area with periodically varying intensities of different colored lights. The intensity of the artificial illumination is controlled by placing resistance bars in series with the sources of illumination, thereby resulting in a very inefficient use of the electrical energy provided from the source.
Krenke, in U.S. Pat. No. 3,210,611, discloses an electrooptical control circuit which is designed to control the flow of electrical energy to an artificial source of illumination responsive to the long-time averaging of the ambient or incident light as opposed to transient light changes. The time delay circuit eliminates changes in the flow of electrical energy to the source of artificial illumination responsive to rapid lighting fluctuations such as would be exhibited by the passage of a cloud in front of the sun. This electrical system does not provide for a dead zone or zone of acceptable lighting intensity, but instead automatically supplies electrical energy to the source of illumination if the ambient illumination falls below a predetermined limit for a selected period of time.
Mas, in U.S. Pat. No. 3,180,978, discloses an illumination system which includes a wall-mounted window having a source of artificial illumination emanating from behind the normal ceiling-mounted illumination. An outside photosensor detects the intensity of external illumination and correspondingly adjusts the backlighting on the artificial window to produce similar lighting for the room, thereby simulating the normal variations in the intensities of natural lighting. The electrical control circuit may also be coupled to the overhead lights for supplying power thereto when the external natural illumination falls below a predetermined limit. This system controls internal illumination responsive to external illumination, but does not control the artificial illumination so as to supplement external natural illumination.
Del Zotto, in U.S. Pat. No. 3,629,649, discloses a photodiode comprising one leg of a resistance bridge, with the intensity of illumination incident upon the photodiode controlling the operation of a latching relay which supplies electrical power to artificial sources of illumination. This system does not control the intensity of the artificial illumination, but merely turns the source of artificial illumination on and off.
Crozier, in U.S. Pat. No. 3,878,439, discloses a photo-transistor which is coupled to a Schmidt trigger acting as a threshold detector for supplying electrical energy to a relay which in turn couples a load to a source of electrical energy. A timing circuit is provided for starting the operation of the relay when the phototransistor changes from an illuminated condition to a non-illuminated condition, or vice versa.
Bolhuis, in U.S. Pat. No. 3,863,104, discloses a lighting control system for being utilized with at least two groups of electrically powered lamps, such as those utilized in transportation tunnels. Each of the groups of lamps is independently controlled, but not responsive to a level of ambient illumination.
Charles, in U.S. Pat. No. 3,767,924, discloses an electrical make and break switch for use in controlling the lighting in a modern office building or school responsive to signals from a computer. Independent control of the lights is obtained through the computer and also from local stations by the utilization of photosensitive detectors at the local stations. McCabe, in U.S. Pat. No. 3,249,805, discloses a signal controlled rectifier (or silicon controlled rectifier-SCR) of the type which could be used for controlling the flow of electrical energy to a load.
Reference is also made to a device in a pending United States patent application in the name of the National Aeronautics and Space Administration which includes a bidirectional mechanical motor which actuates serial switches for sequentially applying electrical energy to artificial sources of illumination. This device includes a plurality of mercury switches which are located about the circumference of a circular plate. The plate is rotated by the motor in steps responsive to the level of illumination incident upon a photocell. This patent application was filed on Dec. 23, 1976, and accorded the Ser. No. 753,977.
These prior art references are illustrative of the many similar references located generally in the following classes/subclasses of U.S. Patent Office: 362/1, 20, 85, 147; 361/173, 174, 175, 197; 250/214 AL, 239; 307/116,117, 124,132 T, 311; 315/151, 153, 156, 158, 159, 149, 150, 152, 155, and others.
The prior art also includes various existing designs which utilize a 555 timer having the inputs thereof shorted until the level of illumination crosses an unacceptable threshold limit. The inputs are then coupled to an R-C network having the appropriate time constant for determining the timing period. If at anytime during the timing period the level of illumination recrosses the illumination threshold, then the inputs of the clock timer are again shorted to ground. One limitation of this design appears when the voltage across the R-C network exceeds approximately 38 percent of the trigger voltage for the 555 device. Under these circumstances the noise impulse created by shorting the R-C network to ground generally will trigger the 555 device, thereby producing a false timing pulse which typically will produce a false change in the level of artificial illumination. In contrast with this design, the present invention utilizes a continuous clock and separate sampling gates which are periodically clocked to sample the levels of illumination and responsive thereto an error signal is generated. The use of a continuous clock with periodic sampling tends to eliminate the false triggering inherent in the aforementioned prior art designs.